Implanted cardiac defibrillators are known, in which the high voltage capacitors are discharged to provide a defibrillating high energy shock that is timed off the sensed electrogram. However, if there is a mistaken diagnosis by the device and the shock is delivered into sinus, it is particularly arrhythmogenic if it is asynchronous and happens to coincide with the vulnerable zone. Further, if the rhythm converts back to sinus rhythm, we have found that the shock should be aborted since even a synchronous shock carries some risk.
Present implantable defibrillators that are sold by CPI/Intec are committed to deliver a high voltage shock once the capacitors begin charging. Thus after charging is completed, the high voltage shock will necessarily be delivered. Likewise, the implantable cardioverter that was sold by Medtronic, Inc. was also committed to deliver the high voltage shock once the capacitors begin charging.
In the implantable defibrillator presently sold by Telectronics, Inc., during charging of the capacitors the charging is discontinued part way to recheck the arrhythmia status. However, independent of the result of that arrhythmia check, the capacitors continue charging and an arrhythmia check is made again when the capacitors are fully charged. Only if both checks show an arrhythmia, do the capacitors deliver the high voltage shock to the heart.
It is an object of the invention to provide a cardiac defibrillation method in which the high voltage shock does not coincide with the vulnerable zone.
Another object of the present invention is to provide a cardiac defibrillation method in which the high voltage shock is aborted if the arrhythmia converts back to sinus rhythm.
Other objects and advantages of the invention will become apparent as the description proceeds.